Optical coherence tomography (OCT) is an optical signal acquisition and processing method. It captures micrometer-resolution, three-dimensional images from within optical scattering media (e.g., biological tissue). Optical coherence tomography is an interferometric technique, typically employing near-infrared light. The use of relatively long wavelength light allows it to penetrate into the scattering medium.
Light in an OCT system is broken into two arms—a sample arm (containing the sample) and a reference arm (usually a mirror). The combination of reflected light from the sample arm and reference light from the reference arm gives rise to an interference pattern if light from both arms has traveled the “same” optical distance (“same” meaning a difference of less than a coherence length).
By scanning the mirror in the reference arm, a reflectivity profile of the sample can be obtained. Areas of the sample that reflect back a lot of light will create greater interference than areas that don't. Any light that is outside the short coherence length would not interfere. This reflectivity profile, called an A-scan, contains information about the spatial dimensions and location of structures within the sample. A cross-sectional tomograph (B-scan) may be achieved by laterally combining a series of these axial depth scans (A-scan). En face imaging at an acquired depth is possible depending on the imaging engine used.